CO2 and O2 removal during continuous veno-venous hemofiltration: a pilot study

Abstract

Background Carbon dioxide (CO 2 ) accumulation is a challenging issue in critically ill patients. CO 2 can be eliminated by renal replacement therapy but studies are scarce and clinical relevance is unknown. We prospectively studied CO 2 and O 2 behavior at different sample points of continuous veno-venous hemofiltration (CVVH) and build a model to calculate CO 2 removal bedside. Methods In 10 patients receiving standard CVVH under citrate anticoagulation, blood gas analysis was performed at different sample points within the CVVH circuit. Citrate was then replaced by NaCl 0.9% and sampling was repeated. Total CO 2 (tCO 2 ), CO 2 flow (V̇CO 2 ) and O 2 flow (V̇O 2 ) were compared between different sample points. The effect of citrate on transmembrane tCO 2 was evaluated. Wilcoxon matched-pairs signed rank test was performed to evaluate significance of difference between 2 data sets. Friedman test was used when more data sets were compared. Results V̇CO 2 in the effluent (26.0 ml/min) correlated significantly with transmembrane V̇CO 2 (24.2 ml/min). This represents 14% of the average expired V̇CO 2 in ventilated patients. Only 1.3 ml/min CO 2 was removed in the de-aeration chamber, suggesting that CO 2 was almost entirely cleared across the membrane filter. tCO 2 values in effluent, before, and after the filter were not statistically different. Transmembrane tCO 2 under citrate or NaCl 0.9% predilution also did not differ significantly. No changes in V̇O 2 were observed throughout the CVVH circuit. Based on recorded data, formulas were constructed that allow bedside evaluation of CVVH-attributable CO 2 removal. Conclusion A relevant amount of CO 2 is removed by CVVH and can be quantified by one simple blood gas analysis within the circuit. Future studies should assess the clinical impact of this observation. Trial registration The trial was registered at https://clinicaltrials.gov with trial registration number NCT03314363 on October 192,017. Electronic supplementary material The online version of this article (10.1186/s12882-019-1378-y) contains supplementary material, which is available to authorized users.

The effect of age and body mass index on energy expenditure of critically ill medical patients

“…Second, we have excluded patients on RRT, because we did not conduct IC with and without RRT in order to rule out the possible influence of RRT on gas exchange, particularly CO 2 . A recent pilot study on ten patients reported on a relevant CO 2 elimination with continuous veno-venous hemofiltration [37]. However, its implication on IC has to be validated.…”

MECCIAS trial: Metabolic consequences of continuous veno-venous hemofiltration on indirect calorimetry

“…During saline predilution True REE was 1604 ± 633 kcal/d which was statistically different from baseline (p ¼ 0.014) but not when compared to "without CVVH" (p ¼ 0.432). [11]. This increased during high dose settings to 37.7 mL/min.…”

“…As these values are subsequently used to calculate REE, this implicates that any therapy that adds or removes CO 2 and/or O 2 from the circulation may produce dubious results and preclude a correct use of IC [6,7]. Continuous renal replacement therapy (CRRT), which is widely used in critically ill patients with acute kidney injury [8e10], also removes CO 2 [11]. Previous observations suggest that intermittent hemodialysis and peritoneal dialysis do not change REE [12].…”

“…We previously described a method to quantify CO 2 removal during continuous veno-venous hemofiltration (CVVH) based on one simple blood gas analysis within the circuit [11]. The aims of our interventional study are twofold: first, to explore how CRRTrelated CO 2 removal influences V_CO 2 and REE measured via IC and second, to study the effect of CVVH with citrate anticoagulation on REE, V_CO 2 and V_O 2 .…”

Extracorporeal CO₂ Removal Integrated within a Continuous Renal Replacement Circuit Offers Multiple Advantages

“…In a recent study, Jonckheer et al [26] measured the levels of CO 2 and O 2 pre- and postfilter and in the effluent in patients treated with CRRT under standard conditions. The VCO 2 drops significantly between the prefilter and the postfilter measurements (from 110.5 ± 9.6 mL to 84.5 ± 6.5 mL/min [ p > 0.01]).…”